Late Reflections, Echoes, and Speech Intelligibility

02 Nov Late Reflections, Echoes, and Speech Intelligibility

While human ears and brains are remarkable speech processors, our ability to understand speech is easily degraded by a little background noise or a distorted speech signal.

Late Reflections and Listeners

One of the most damaging distortions to a speech signal is a reflection, or a series of reflections, that arrives after the direct speech signal. These late reflections, when loud enough, can mask subsequent direct speech signals. For listeners, this can render speech unintelligible. You might have encountered this phenomenon at an outdoor sporting venue, where signals from several loudspeakers arrive at your seat at different times, piling words and phrases onto each other in a garbled heap.

Late Reflections and Talkers

As difficult as late reflections are for listeners, they can also cause problems for talkers. To successfully speak over these echoes, talkers need to concentrate and time their words to fall between the reflections.

Have you ever experienced a long-distance phone conversation with echoey reception? It’s unnerving to hear yourself through the earpiece with a noticeable delay. And if the line echo were loud enough, you might find yourself repeating words or changing your cadence.

Semicircular Situations

In the world of architecture, late reflections can occur in a room that’s designed as a semicircle, with the talker at the centre of the radius. This is a common design for churches, where the pulpit is stationed near the focal point. In these cases, the pastor may have to speak through a late reflection that’s audible to only him. For a room that’s 40 to 75 feet deep, reflections can arrive between 80 to 150 milliseconds after the direct signal. While the congregation might be unaware of the pastor’s struggle to speak around the echoes, they will be aware of odd pauses or strange rhythms in the delivery of the sermon.

Eliminating Late Reflections Through Acoustical Design

At BKL, using the latest instruments and computer software, we can detect and analyze reflections as separate signals when they are delayed more than 80 milliseconds. We also create 3-D models of rooms to simulate potential problematic reflections. For new builds or existing rooms, we can make recommendations for positioning walls and ceilings, and adding absorptive or diffusive finishings to control reflections and optimize the space for its intended use. Get in touch with us today if you want to learn more about eliminating late reflections at your facility or designing a new build so it has the best acoustics possible.